1. Field of the Invention
The present invention relates to a control technique at the time of executing a plurality of calibrations together in an image forming apparatus.
2. Description of the Related Art
In recent years, accompanying the trend of computerization, the need to output a document and an image in color is spreading and printers of various kinds of systems are put on the market. The systems for forming a color image include the sublimation system, the thermal transfer system, the inkjet system, etc., however, from the viewpoint of forming an image quickly, the electrophotographic system is said to be the most excellent.
However, the image forming apparatus of electrophotographic system has such a problem that the density of an image varies considerably depending on the use environment (temperature and humidity), the variation in the characteristics of photoreceptor and developer, and the durability state of the developing equipment etc. In particular, the color image forming apparatus has such a problem that the color tone also changes.
To address these problems, a calibration using a one-dimensional LUT (Look Up Table) for density correction corresponding to the “single color” of cyan, magenta, yellow, and black (hereinafter, described as C, M, Y, and K) is executed conventionally. The LUT is a table indicating output data corresponding to input data separated into specified intervals and enables representation of nonlinear characteristics that cannot be expressed by an arithmetic operation expression. The one-dimensional LUT for density correction includes printer-side output signal values capable of representing the input signal value of each of CMYK and an image is formed on a sheet using the toner corresponding to the output signal value. First, a chart including data at different densities corresponding to the toner of each of CMYK is prepared and output in a printer unit. Then, by reading the value of the output chart with a scanner or colorimeter and by comparing the read value with the target data possessed in advance, the one-dimensional LUT for density correction for each of CMYK independently of one another. Hereinafter, the calibration for each color independent of one another is called the “single color calibration”.
However, even by adjusting the density characteristic of a single color by the one-dimensional LUT, a “multi color” causes a nonlinear difference depending on the printer, and therefore, it is difficult to guarantee the color tone. Here, the “multi color” is a color using toner of a plurality of colors, such as red, green, and blue using two colors of C, M, and Y, gray using C, M, and Y, etc. In particular, in the electrophotographic system, even by correcting the gradation characteristic of a single color by the one-dimensional LUT, in the case where a “multi color” is represented using toner of a plurality of colors, a nonlinear difference is caused frequently. Because of this, by executing a calibration, the color reproduction characteristic of a multi color represented by a combination (superimposition etc.) of toner of a plurality of colors is corrected. For example, the technique to correct a color difference of a multi color by focusing attention on the destination profile of the ICC profile and by modifying the profile has been proposed (see Japanese Patent Laid-Open No. 2006-165864). The ICC profile is the data specified by the ICC (International Color Consortium) and used at the time of color conversion. First, a chart created by a multi color is output by a printer and the chart is measured with a scanner or colorimeter. Then, a difference is created using the colorimetry result and the target value and a three-dimensional LUT (destination profile) for converting a device-independent color space (L*a*b*) of the ICC profile into a device-dependent color space (CMYK) is updated. Due to this, it is made possible to correct the reproduction characteristic of a multi color. Hereinafter, the calibration for such a multi color is called the “multi color calibration”. The L*a*b* is one of device-independent color spaces and L* represents luminance and a*b* represent hue and saturation. Further, as the technique to correct the reproduction characteristic of a multi color, the calibration technique has also been proposed, in which a chart created by a multi color in the range that can be reproduced by a printer is output and the chart is measured with a scanner or colorimeter, and then, the measured value is compared with the target value and thus the correction value is created (see Japanese Patent Laid-Open No. 2011-254350).
Then, the calibrations the correction targets of which are different should be executed individually for each calibration, however, there are apparatuses equipped with the function to combine those calibrations and to execute the calibrations continuously. Hereinafter, the function to continuously execute a plurality of calibrations the correction targets of which are different is called the “continuous calibration function”. Once such a continuous calibration is started, it is no longer possible to do a job accompanied by printing, and therefore, there is a possibility that the printing chances are lessened. To address this, it has been proposed to abort the calibration in the case where the accumulated number of printed sheets to which the number of sheets related to the printing of image data is added is less than a fixed number, and to continue the calibration in the case where the number is equal to or more than the fixed number (see Japanese Patent Laid-Open No. 2011-022231).
In the conventional mechanism, in the case where a request for printing is made, calibration processing being currently performed is aborted by giving instructions to cancel. Because of this, it is necessary to wait until the execution of a calibration is started in order to cancel the calibration.